1. Field of the Invention
This invention relates to golf balls (including solid golf balls and wound golf balls).
2. Prior Art
The most requisite characteristic for golf balls is a long flight distance. Heretofore, a number of proposals have been made for the purpose of increasing flight distance. However, most of the proposals intend to increase the flight distance in the high-speed region of high head speeds while little attention is paid to the flight distance in the low-speed region of low head speeds. As a consequence, there is a tendency that the ball receives favorable lift and drag in the high-speed region, but in the low-speed region, the ball receives a drastically increased drag so that the ball becomes unstable on fall, or a drastically decreased lift so that the ball drops.
In this regard, golf balls targeted for players with a relatively low head speed for ensuring increased flight distance were proposed. These golf balls, however, tend to sky in the high-speed region because of the excessive lift.
As understood from above, it occurred to few engineers in the art to develop a golf ball adapted to receive optimum lift and drag over a wide range from low to high-speed regions, especially by paying attention to the dimples that affect the lift and drag on the ball.
Therefore, an object of the invention is to provide a golf ball adapted to receive stable satisfactory lift and drag over a wide range from low to high-speed regions and travel a satisfactory distance at both low and high head speeds.
Making extensive investigations in order to achieve the above object and analyzing numerous data, the inventor discovered that although various proposals were made regarding the overall dimple volume and other indexes associated with the design of dimples, merely specifying the overall dimple volume failed to afford satisfactory lift and drag over a wide range from low to high-speed regions. With the discovery that when one dimple is considered, the influence on lift and drag of a small-diameter portion on the bottom side differs from the influence on lift and drag of a large-diameter portion on the upper side, the inventor has found that it is effective to introduce the concept of dimple operative volumes which are obtained by assuming different dimple operative coefficients to the large-diameter portion on the upper side and the small-diameter portion on the bottom side and multiplying the volumes of the large-diameter portion and small-diameter portion by the respective coefficients.
Making further investigations, the inventor has found that even the identical dimple has different dimple operative coefficients between the high-speed region with head speeds above 46 m/s and the low-speed region with head speeds below 38 m/s; that when the dimple operative volume of each dimple is determined by setting the dimple operative coefficients for the high-speed region and the low-speed region at specific values as will be described later, slicing the dimple as will be described later, and multiplying the volume of a slice by the coefficient, the sum of dimple operative volumes for all the dimples is set to fall within a specific range, and especially the sum of high-speed region dimple operative volumes obtained using the dimple operative coefficients for the high-speed region is set to fall within a specific range, whereby stable satisfactory lift and drag are available over a wide range from low to high-speed regions. It has also been found that when the sum of low-speed region dimple operative volumes is set to fall within a specific range, more preferably when the ratio of the sums of dimple operative volumes is set to fall within a specific range, and when along with the foregoing factors, the overall dimple volume is optimized, the above effects are more advantageously achieved.
Therefore, the invention provides a golf ball as defined below.
(1) A golf ball having a plurality of dimples formed in its surface, characterized in that the sum of high-speed region dimple operative volumes of respective dimples as calculated by the method to be described later is 210 to 310.
(2) The golf ball of (1) wherein the sum of low-speed region dimple operative volumes of respective dimples as calculated by the method to be described later is 210 to 310.
(3) The golf ball of (2) wherein the ratio of the sum of high-speed region dimple operative volumes to the sum of low-speed region dimple operative volumes is from 0.8/1 to 1.0/1.
(4) The golf ball of any one of (1) to (3) wherein the overall dimple volume is 250 to 400 mm3.
(5) The golf ball of any one of (1) to (4) comprising a solid core formed of a rubber composition to a diameter of 34 to 40 mm and a cover enclosing the core.
(6) The golf ball of (5) wherein the cover has two or three layers.